This invention relates to machine tools and more particularly to an improved pipe beveling tool.
Larger diameter pipes are often machined by a pipe beveling and facing tool to provide a surface suitable for welding pipe fittings or other pipe thereto. Such pipe beveling tools generally have a pipe attachment unit, a drive unit, a feed unit and a cutting unit.
The pipe attachment unit typically is a mandrel that has at one of its ends a chuck with expandable jaws. A draw bolt is provided such that when the draw bolt is rotated, the jaws of the mandrel chuck radially expand uniformly from the chuck body, thereby frictionally engaging the inner walls of the pipe to be machined. This frictional engagement provides a strong, stable attachment such that the mandrel is oriented along the longitudinal axis of the pipe to be beveled. On the mandrel is supported a drive unit, a feed unit, and a cutting unit of a pipe beveling tool.
The drive unit is non-rotatable and is slideably mounted on the mandrel. The drive unit rotates a cutting unit which holds cutting bits capable of performing such machining procedures as xe2x80x9cfacingxe2x80x9d, xe2x80x9cbevelingxe2x80x9d or xe2x80x9cradiusingxe2x80x9d the pipe. The drive unit and cutting unit are advanced axially along the mandrel toward the pipe by a feed unit which connects the drive unit to the mandrel. In operation, a reactionary force (counter torque) is transmitted to the drive and feed units as the rotating cutting unit performs machining operations on the pipe. The drive and feed units however, do not rotate because they are locked to the mandrel which is held from moving relative to the pipe by the mandrel chuck.
A common area of difficulty with conventional pipe beveling and facing machines is that to change cutter heads or cutter tool bits, the pipe attachment unit must be removed from the inside of the pipe. This is time consuming and can lead to a loss of alignment upon reinstallation.
Another problem with prior art devices in this field is that they do not render a smoothly machined surface. This is a result of xe2x80x9cchatterxe2x80x9d or non-uniform application of pressure by the tool bit upon the pipe such that the bit will xe2x80x9cbouncexe2x80x9d and cause an irregular cutting of the pipe surface. This xe2x80x9cchatterxe2x80x9d is caused primarily by backlash and mandrel flex.
Since the mandrel acts as the support for the drive unit, feed unit and cutting unit, all forces generated during the machining operation are transmitted to the mandrel. Therefore the mandrel must be strong enough to maintain sufficient axial rigidity to minimize mandrel flex under cutting conditions. This mandrel flex is partially caused by the combined mass of the feed, drive and cutting units. The longer the distance between the mandrel attachment point and the center of mass of the combined feed, drive and cutting units, the stronger the mandrel must be to provide adequate support. Prior art devices tend to either use a mandrel that is not of sufficient strength, or to position the center of mass of the combined various units of the tool too far from the mandrel attachment point.
Mandrel flex is also partially a problem related to the strength of the holding force that the mandrel chuck exerts on the interior of the pipe. If this holding force is not strong enough to hold the mandrel rigid, when cutting occurs, the forces exerted back upon the mandrel will cause the mandrel chuck to move slightly, resulting in chatter and a reduction in the smoothness of the machined surface. Many of the conventional mandrel chucks do not develop sufficient holding force or there is no method of manipulating the mandrel chuck to develop sufficient holding force.
Another source of chatter in the prior art is from backlash that occurs at the interface between the pipe attachment unit and the drive unit. In high torque situations, such as beveling and facing operations, backlash or relative movement during engagement between the components of the tool is highly undesirable as it causes xe2x80x9cchatterxe2x80x9d. This backlash between various components relative to one another, also accelerates wear, thus, backlash is a self-propagating phenomena. Backlash is a common problem in the prior art because of the way in which the mandrel connects to the rest of the tool. Traditionally, mechanical keys are used to frictionally lock the mandrel and the rest of the tool from moving relative to each other. Conventional keys in the mechanical industry are of a single piece design and not adjustable. To accommodate a friction fit installation, these keys must be designed with somewhat relaxed tolerances so there is inherently a small degree of backlash present wherever mechanical keys are used. Most of the locking keys in the prior art do not compensate for wear, requiring frequent replacement. This conventional design for mating of the mandrel to the rest of the tool thus results in xe2x80x9cchatterxe2x80x9d and also a greater potential for key failure from the high shear stresses resulting from the counter rotational forces.
In order to obtain a sufficiently strong attachment between the mandrel chuck and the pipe, conventional pipe beveling machines have used an elongated chuck design with long jaws that provide a linear frictional engagement with the pipe inner wall. This design limits the use of the pipe beveling tool to situations where sufficient depth exists in the pipe to accommodate this elongated head. Such a design is especially disadvantageous when the machining operation must take place close to a xe2x80x9cTEExe2x80x9d or elbow in the pipe where there may not be sufficient depth to engage the mandrel chuck in the pipe.
Another problem with such prior art tooling devices is their size and weight. Many of these devices are configured with a large percentage of the weight of the device such a distance away from the surface to be machined that the mandrels and chucks must be made thicker and stronger to support the weight. Since these tools are usually operated by a solo operator, weight is important. In an attempt to reduce overall weight, the prior art beveling tools commonly used pneumatic motors which causes another problem, since while pneumatic motors provide the capability for variable speed, high RPMs and high torque, they have the downfall of generating noise from the spinning motor as well as from the pneumatic exhaust. This can be annoying to the operator running pipe machining tools in confined spaces where the noise is intensified and can be damaging to the operator""s hearing.
In accordance with the invention, an improved pipe facing and beveling tool is provided that has a shorter and lighter pipe attachment unit, minimal backlash, a method for changing cutter heads without removing the pipe attachment unit from the inside of the pipe, and a reduced level of operating noise.
Accordingly, it is an object of the present invention to provide an improved pipe beveling tool possessing greater rigidity to minimize mandrel flex during operation.
It is a further object of the present invention to provide an improved compact, lightweight pipe beveling and facing tool that provides a smoothly machined surface, accommodates component wear, and operates with a minimum of chatter.
It is another object of the present invention to provide an improved pipe beveling tool which allows for a maximum of infeed while maintaining a center of mass that is relatively close to the pipe to retain mandrel rigidity.
It is a further object of the present invention to provide an improved design for securing a drive unit to a mandrel so as to minimize backlash and to adjustably compensate for wear of the components.
It is yet a further object to provide an improved compact pipe beveling and facing tool that operates with a reduced level of frictional noise generated from the spinning motor as well as from the pneumatic exhaust encountered during motor operation.
It is another object of the present invention to provide an improved pipe beveling and facing tool with an enhanced method for increasing the frictional engagement of the mandrel chuck head to the inside of the pipe.
It is still another object of the present invention to provide an improved tool with a shorter mandrel chuck capable of providing strong enough frictional attachment to be used with a minimum of pipe depth such as encountered at pipe elbows.
It is further another object of the present invention to provide an improved mandrel chuck that can be used at pipe elbow locations.
It is a still further object of the present invention to provide an improved tool that is more compact, lighter, and has a shorter mandrel than conventional pipe beveling tools.
It is another object of the present invention to provide an improved tool with the ability to change cutter heads or cutter tool bits without removing the mandrel chuck from the pipe.
It is yet another object of the present invention to provide an improved quieter muffler system that encloses and quiets the motor portion of a tool as well as the exhaust.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.